The present invention relates to the selective raising and/or lowering of patient temperatures, and more particularly, to systems and methods for controlling a patient""s temperature via the circulation of heated/cooled fluid through one or more pads contacting a patient.
The use of contact pad systems for selectively cooling and/or heating bodily tissue is known. In such systems a fluid, e.g. water or air, is circulated through one or more pads to affect surface-to-surface thermal energy exchange with a patient. One highly effective contact pad and related system is disclosed in U.S. Pat. No. 6,197,045, hereby incorporated by reference in its entirety. As noted in the ""045 patent, the ability to establish and maintain intimate pad-to-patient contact is often of key importance to fully realizing medical efficacies with contact pad systems.
In this later regard, the effect of temperature on the human body has been well documented. Elevated temperatures, or hyperthermia, may be harmful to the brain under normal conditions, and even more importantly, during periods of physical stress, such as illness or surgery. Conversely, lower body temperatures, or mild hypothermia, may offer some degree of neuroprotection. Moderate to severe hypothermia tends to be more detrimental to the body, particularly the cardiovascular system.
Temperature management, or thermoregulation, can be viewed in two different ways. The first aspect of temperature management includes treating abnormal body temperatures, i.e. cooling the body for elevated temperatures, or warming the body for lowered temperatures. The second aspect of thermoregulation is an evolving treatment that employs techniques that physically control a patient""s temperature to provide a physiological benefit, such as cooling a stroke patient to gain some degree of neuroprotection.
Hypothermia may occur for a variety of reasons, including exposure to cold environments, brain injury, or complex surgical procedures. During surgery, a patient typically experiences mild hypothermia as a result of the effect of general anesthesia on the body""s thermoregulatory system and prolonged exposure of internal organs. Mild hypothermia in the medical or the surgical patient has been thought to prolong the time to extubation, contribute to coagulopathies, increase the chance of infection, and increase cardiac demand as a result of shivering.
Hyperthermia may occur as a result of systemic inflammatory response, sepsis, stroke, or other brain injury. While the mechanism of the effect of the hyperthermia on the brain is not clearly understood, there is evidence to indicate that even mild increases in temperature may contribute to neurological deficits. Hyperthermia also increases the metabolic rate and may deplete energy stores in the body.
In view of the foregoing, it may be appreciated that recognized medical applications for contact pad systems are ever-increasing. By way of example, cooling pad systems may be utilized in early therapy to reduce neurological damage incurred by stroke and head trauma patients. Additional applications include selective patient heating/cooling during surgical procedures such as cardiopulmonary bypass operations.
As these and other medical applications have evolved, the present inventors have recognized the desirability of enhancing the predictability, responsivity, flexibility and portability of thermal exchange pad systems. More particularly, while known heating/cooling contact pad systems have proven effective for many applications, the present inventors have recognized that additional performance objectives and potential applications can be realized via the implementation of further improved control systems and associated control methodologies.
In particular, one objective of the present invention is to provide an improved patient temperature control system and method that provides rapid heating/cooling capabilities via one or more interconnectable contact pads while also yielding size, weight and operating efficiencies.
Another objective of the present invention is to provide an improved patient temperature control system and method that offers high thermal exchange reliability while accommodating application flexibility via the interconnectability of either one or a plurality of contact pads.
An additional objective of the present invention is to provide an improved patient temperature control system and method that facilitates ready set-up and portability.
A further objective of the present invention is to provide an improved patient temperature control system that yields enhanced wear and performance of one or more interconnectable contact pads.
Yet a further objective of the present invention is to provide an improved patient temperature control system and method that enhances patient comfort.
One or more of the above objectives and additional advantages may be realized by utilizing the temperature control system features and associated methods disclosed hereinbelow. The system features may include at least one heat exchanger for affecting at least one of heating and cooling a fluid, a circulating pump for circulating the fluid through the heat exchanger, and at least one interconnectable patient contact pad to affect heat transfer therebetween. For purposes hereof, the term xe2x80x9ccontact padxe2x80x9d refers to any type of pad through which fluid may be flowed from an input port to an output port and which is otherwise adapted to contact a patient to affect heating or cooling.
In one aspect, the inventive system may also include at least a first fluid reservoir, or xe2x80x9cmake-up fluid reservoirxe2x80x9d, fluidly interconnectable with the contact pad(s). The first fluid reservoir may be utilized to contain fluid that is removable from the reservoir to fill/circulate through the pad(s) during use. In conjunction with this aspect, the system may be defined so that, during normal heating/cooling operations, fluid is circulatable through the pad(s) and the heat exchanger(s) by the circulating pump substantially free from passage through the first fluid reservoir. By virtue of this arrangement, rapid fluid temperature changes may be achieved in the system since only the circulated fluid is temperature controlled (e.g., not any additional fluid remaining within the first fluid reservoir during fluid circulation). Relatedly, reduced heat exchanger requirements may be realized. Further, flexibility may be maintained by containing a fluid volume in the first reservoir that is sufficient for filling a plurality of interconnectable contact pads.
Preferably, the system also comprises a second fluid reservoir, or xe2x80x9ccirculating fluid reservoirxe2x80x9d, through which fluid is circulated during normal heating/cooling operations. In that regard, the first and second reservoirs may be directly, fluidly interconnected so that fluid may be removed from and flowed back into the first fluid reservoir via passage through the second fluid reservoir. Further, the heat exchanger, circulating pump and first and second fluid reservoirs may be supportably located within a common housing, wherein the system is substantially self-contained to facilitate portable use.
More particularly, all or at least a portion of the first fluid reservoir may be physically located above the second fluid reservoir to provide for gravity fluid flow from the first reservoir to the second reservoir. Relatedly, the top of the first reservoir may be maintained at substantially atmospheric pressure (e.g. via a vent having a semi-permeable filter), wherein gas may be removed from/passed into the system. Further, a sensor may be provided at the second fluid reservoir for sensing the amount of fluid contained by the second reservoir, wherein a user output may be provided if/when the fluid amount drops below a predetermined amount.
For example, the sensor may provide an output signal to a controller (e.g. a microprocessor), wherein the controller transmits a signal to a user out put (e.g. a display and/or audible output device). Such user output may not only alert a user of the condition but may also advise the user regarding fluid refilling procedures. Further, the controller may automatically turn-off the circulating pump and heat exchanger if/when the sensed fluid amount in the reservoir drops below a predetermined level.
In further relation to the above-noted aspect, the first fluid reservoir and second fluid reservoir may be provided to contain first and second fluid volumes, respectively, of the fluid present within the system (e.g. when the system is fluidly disconnected from the interconnectable pads), wherein the first fluid volume is greater than the second fluid volume. Preferably, the first fluid volume is between about 3% and 50% of the first fluid volume. As may be appreciated, the interconnectable contact pad(s) may have an internal volume greater than the second fluid volume, wherein at least some of the fluid contained in the first fluid reservoir may be flowed out of the first reservoir for circulation through the pad(s) during heating/cooling. The amount of fluid removed from the first reservoir for such purpose(s) will depend on the number of pads that are interconnected.
In conjunction with the foregoing, it may appreciated that an inventive temperature control method is provided that includes the steps of containing a fluid in a first fluid reservoir and flowing at least a portion of that fluid out of the first reservoir, wherein the removed portion is circulated through at least one interconnected contact pad and a heat exchanger fluidly interconnected therewith, substantially free passage through the first reservoir. In turn, the method further comprises the step of contacting the pad(s) to a patient to affect heat transfer therebetween. Typically, an amount of fluid corresponding with the removed portion is returned to the first fluid reservoir, e.g. upon completion of a given patient heating/cooling procedure.
The method may further include the step of selectively establishing the fluid interconnection of the contact pad(s). In this regard, it is contemplated that the method may be practiced utilizing a system that may be selectively and readily interconnected to and disconnected from one or a plurality of contact pads, as deemed appropriate by medical personnel for heating/cooling a patient in a given situation. For such purposes, the method may further provide for holding a first fluid volume in the first fluid reservoir and a second fluid volume in a second fluid reservoir, wherein the first and second fluid volumes are combinatively sufficient to fill a plurality of contact pads. Preferably, the amount of fluid present in the second fluid reservoir may be sensed, wherein a sensor output signal is employable to provide a user output (e.g. when the fluid level drops below a preset amount), as noted above.
The described system and method may also provide for drawing the circulated fluid through the interconnectable contact pad(s) under negative pressure. Such negative pressure may be established by locating the circulating pump downstream of the pad(s), wherein fluid is pumped out of the pad(s) and then through the heat exchanger into the second fluid reservoir. As noted, the second fluid reservoir may be maintained at substantially atmospheric pressure. Preferably, the inventive method may further provide for locating the interconnected contact pad(s) above the first and second fluid reservoirs. Such location facilitates fluid flow out of the interconnectable contact pad(s) and back into the system, e.g. in the event of pad leakage/pump stoppage.
In another aspect, an inventive temperature patient control system is provided which includes not only a circulating pump and at least one heat exchanger, but additionally a pressure sensor fluidly interconnected between an inlet side of the circulating pump and an outlet port of the interconnectable contact pad(s). The pressure sensor may provide an output pressure signal employable to control the circulating pump. Again, the circulating pump may be disposed to establish a negative pressure in the interconnectable contact pad. In turn, the output pressure signal may be employed to control the circulating pump so as to maintain the negative pressure within a predetermined range. Such an arrangement facilitates the maintenance of a desired minimum pressure in each of the one or more interconnectable contact pads.
Additionally, the system may include a controller for receiving the output pressure signal from the pressure sensor and for providing a control signal to the circulating pump in response thereto. In the later regard, the control signal may be provided to control the operating speed of the pump. More particularly, the controller may utilize the outlet pressure signal and a predetermined information set (e.g. corresponding with a desired pressure range for the interconnectable contact pad(s)) to control the operating speed of the pump.
The inventive system may also include a flow meter for measuring a flow rate of the fluid between an outlet side of the circulating pump and an inlet port of the interconnectable contact pad(s), wherein the flow meter provides an output flow signal. In turn, a user output device may be included to provide an output in response to the identification of a predetermined relationship between the output flow signal and the pump operating speed and/or the output pressure signal. By way of primary example, such predetermined relationship may correspond with conditions which may indicate the presence of a potential fluid circuit blockage (e.g. a kink in a tubing line used for pad interconnection). The user output may include remedial action information to assist a user in addressing the situation.
In the described system, the flow meter and heat exchanger(s), as well as any other pressure-drop system components (e.g. fluid reservoir(s)) may be preferably located downstream of the circulating pump and upstream of the interconnectable pad(s). By so doing, the desired negative pressure in the interconnectable pads may be more reliably maintained. Again, the noted system components may be supportably disposed in a common housing to yield a self-contained system.
In conjunction with the inventive system noted above, it may be appreciated that a patient temperature control method is provided that includes the steps of operating a circulating pump to circulate a fluid through a heat exchanger and at least one interconnected contact pad, and sensing a pressure of the fluid between an inlet side of the circulating pump and an outlet port of the at least one interconnected contact pad, wherein the sensed fluid pressure is employed in the pump operating step. The operating step may provide for the establishment of a negative pressure in the contact pad(s). Further, an output pressure signal may be provided in relation to the sensed pressure, wherein the output pressure signal is employed in the operating step to maintain the negative pressure within a predetermined range. Such predetermined range may be set in relation to the attributes of the given interconnected contact pad(s) so as to insure a minimum fluid flow sufficient to affect the desired heat transfer while avoiding high pressures that could unduly stress the contact pad(s).
The inventive method may further include the steps of containing at least the portion of the circulated fluid in a fluid reservoir, and maintaining the fluid reservoir at substantially atmospheric pressure. In turn, the maintaining step may provide for a venting of the fluid reservoir, e.g. to the ambient atmosphere.
Additionally, the method may include the step of utilizing the above-noted output pressure signal to provide a control signal to the circulating pump (e.g. via a microprocessor controller), wherein such control signal controls an operating speed of the pump. Further, the method may include the step of measuring a flow rate downstream of the circulating pump and upstream of the inlet port of the interconnected contact pad(s), wherein an output flow signal may be provided (e.g. to controller). In turn, the method may provide a user output in response to the identification of a predetermined relationship between the output flow signal and the pump operating speed and/or the output pressure signal. As noted, such predetermined relationship may be established in relation to conditions which would indicate a blockage in the fluid circuit of the system. The user output may be provided to identify at least one remedial response that may be undertaken by a user.
In an additional aspect, an inventive system is provided that includes a heat exchanger for at least one of heating/cooling a fluid, a circulating pump for circulating a fluid through the heat exchanger and an interconnectable contact pad, and a fluid reservoir which is fluidly interconnectable with the interconnectable pad(s) and which contains at least a portion of the circulated fluid. Of importance to this aspect, the fluid reservoir is internally maintained at substantially atmospheric pressure. For such purposes a vent may be interconnected to the fluid reservoir, such vent having a porous, hydrophobic membrane to permit gas passage and restrict fluid passage therethrough. Further, the circulating pump may be disposed to establish a negative pressure in the interconnectable pad(s). Such an arrangement facilitates reliable fluid passage through the contact pad(s) and minimizes fluid leakage in the event the pad(s) is punctured or otherwise breached.
A vent line may also be provided between the noted vent (e.g. at the fluid reservoir) and an outlet side of the fluid reservoir. Further, a vent valve may be provided for opening and closing the vent line, wherein upon opening the vent line gas is free to pass through the vent line and the interconnectable contact pad(s) in response to the negative pressure established therewithin. Preferably, the vent line is interconnected to a top end of the fluid reservoir.
For purposes of opening/closing the vent valve a controller may also be provided. Relatedly, a user interface may be included for receiving user input instructions for operation of the controller. That is, for example, a user may operate the system in one mode of operation in which the vent valve is closed and fluid is circulated through the interconnectable contact pad(s). In another mode of operation the controller may be xe2x80x9cinstructedxe2x80x9d to open the vent valve so that gas is drawn through the at least one interconnectable contact pad(s) to purge fluid therefrom. Such mode of operation may be utilized at the completion of a given patient temperature control procedure. Again, the various system components may be supportably disposed in a common housing.
In view of the foregoing, a further inventive method is also provided that includes the steps of operating a circulating pump to circulate fluid through a heat exchanger, a fluid reservoir and at least one contact pad fluidly interconnected therewith, and maintaining the fluid reservoir at substantially atmospheric pressure. The operating step may provide for the establishment of a negative pressure in the interconnected contact pad. Relatedly, the contact pad(s) may be preferably located above the fluid reservoir.
To purge fluid from the interconnected contact pad(s) the method may further provide for the flowing of a gas though a vent line and into the interconnected contact pad. Such gas flow may be selectively achieved by the opening/closing of a vent valve disposed in the vent line in response to control signals provided by a controller. Again, such control signals may be provided in response to input instructions provided by a user, wherein fluid may be purged in one mode of operation and circulated for heating/cooling in another mode of operation.
In yet a further aspect, a patient temperature control system and method are provided that utilize a heat exchanger, a circulating pump for circulating fluid through the heat exchanger and an interconnectable pad(s), and a fluid bypass line for flowing the fluid from an outlet side of the heat exchanger back to an inlet side of the circulating pump. Such an arrangement allows for the heating/cooling of the circulated fluid free from passage through an interconnectable contact pad(s), e.g. to achieve fluid preconditioning prior to interconnection of or fluid flow through the pad(s). In conjunction with this inventive system/method, a bypass valve may be employed for opening and closing the fluid bypass line. Further, a controller may be provided for supplying control signals to open/close the valve. In turn, the system/method may also utilize a user interface for receiving instructions at the controller, e.g. commands to initiate/terminate fluid conditioning thereby causing the bypass valve to be opened/closed.
In one arrangement, the inventive system may also comprise a fluid reservoir for containing at least a portion of the circulated fluid, wherein the fluid bypass line extends between the fluid reservoir and the inlet side of the circulating pump. Such reservoir may be vented for removing gas from the system as noted above.
Further, a fluid temperature sensor may be utilized for sensing the temperature of the circulated fluid and providing an output temperature signal in response thereto. In turn, such output temperature signal may be utilized in the control of the heat exchanger. For example, a controller may receive the fluid output temperature signal to control the operation of the heat exchanger, wherein the fluid is adjusted to a temperature within a predetermined range. Such range may be set at the user interface noted above. Again the noted system components may be supportably disposed in a common housing.
In yet a further aspect, a patient temperature control system and method are provided that utilize first and second heat exchangers for heating and cooling a fluid, respectively, and a circulating pump for circulating fluid through at least one interconnectable contact pad. A housing is also provided to supportably house the pump and first and second heat exchangers, wherein one of the heat exchangers is selectively interconnectable to an external source for providing one of a heating or cooling medium. By virtue of the noted arrangement, a temperature control system and associated method may be provided with reduced componentry and weight, thereby enhancing affordability. By way of primary example, one of the noted heat exchangers maybe selectively interconnectable with an external fluid refrigeration system that provides a chilled fluid for applications requiring significant fluid cooling.
The inventive system/method may further employ an auxiliary pump for pumping fluid through the heat exchanger that is interconnected with the external source. In turn, a fluid temperature sensor may be provided for sensing the temperature of the system fluid and providing an output temperature signal employable for controlling the operation of the auxiliary pump. In this regard, a controller may also be provided for receiving the output temperature signal and providing a control signal to set the speed of the auxiliary pump, wherein a desired degree of heat transfer with the external source is achieved.
In yet an additional aspect of the present invention, a patient temperature control system and method are provided that utilize a heat exchanger for one of heating and cooling a fluid, a circulating pump for circulating the fluid through the heat exchanger and at least one fluidly interconnectable contact pad, and first and second fluid temperature sensors that are located upstream and downstream, respectively, of the heat exchanger. Such sensors sense the temperature of the circulated fluid and provide first and second temperature output signals. Further, a controller may be employed to utilize the first and second temperature output signals to provide a control signal to the heat exchanger. By virtue of the described arrangement, an amount of heat exchange through the interconnectable contact pad(s) to/from a patient may be determined since the temperature of the fluid flowing to/from the pad(s) is determined. As such, the heat exchanger may be more precisely controlled to achieve targeted patient temperature.
Further in this regard, the system/method may employ a flow meter for measuring a flow-rate of the fluid between the circulating pump and an outlet port to the interconnectable contact pad(s). Such flow meter may provide a flow-rate output signal that is also employable by the controller in the provision of the heat exchanger control signal.
Additionally, the noted system/method may include a controller adapted to receive an input signal indicative of a patient""s temperature and to employ such signal in the provision of the heat exchanger control signal. By way of example, the input may signal may be received from one or more patient core temperature sensors. By way of example, such patient core temperature sensor(s) may compare a nasopharynegeal, esophageal, bladder, tympanic and/or rectal probe(s).
As may be appreciated, various ones of the features noted above may be combined in an optional system. Further, numerous user interface features may be implemented to yield a highly automated and user-friendly system.
Additional aspects and advantages of the present invention will become apparent to those skilled in the art upon consideration of the further description provided hereinbelow.